Federal and State Systems

By now, everyone has seen or otherwise learned that there are both Federal courts and State courts, and that the two operate differently $-$ in some cases very different. The most common time that these systems are seen in play are in drug cases.

Looking at California as an example, we have a case where an individual State has made possession of a drug under certain settings either legal $($under medical needs$)$ or made it a civil violation. As a matter of fact, there are legal growers in the State of California that produce significant quantities. The Federal system still views these individuals as committing a criminal act.

What are your thoughts on incidents where Federal agents have conducted arrests and prosecutions of persons who are conducting activities that are technically "legal" under State law? Do you think that there should be consistency between the two authorities, or do you think that the States should be free to create their own policies?; If so$,$ should the federal government defer to those policies in those states? What are the arguments for and against your position?